An electronic device is required to have two features concerning electrical noise, that is, noise generated by the device is so small that it does not adversely affect other devices and the device does not malfunction even if it receives a certain amount of noise from another device (EMC: Electro-Magnetic Compatibility). In an electronic device that performs wireless communication and an electronic device that performs high-speed operation (e.g., a mobile phone), even if noise generated from another device is cut off, noise generated from those electronic devices may adversely affect the performance of the devices.
For example, in a flip type mobile phone shown in FIG. 5, a cover-side casing 81 contains a liquid crystal module 83, and a body casing 82 contains a CPU 84, a logic circuit 85, a high-frequency circuit 86, a communication antenna 87, etc. To connect the liquid crystal module 83 in the cover-side casing 81 to the CPU 84 in the body casing 82, a flexible printed circuit (hereinafter, referred to as the FPC) 88 is provided therebetween.
The communication antenna 87 radiates electromagnetic waves in accordance with control from the high-frequency circuit 86. Some of the radiated electromagnetic waves affect wirings on the FPC 88 and thus noise is placed on the wirings on the FPC 88. For example, the wirings on the FPC 88 are connected to a liquid crystal module control circuit. If noise is placed on the wirings, then noise is also placed on a counter electrode voltage of a liquid crystal panel through the liquid crystal module control circuit, and accordingly, a liquid crystal applied voltage becomes unstable, degrading the display quality of a liquid crystal screen. As a method to solve this problem, a method is conventionally known in which anti-noise components (e.g., a bypass capacitor or a common-mode choke coil) are provided on signal lines from which the influence of noise is to be eliminated. In the mobile phone shown in FIG. 5, anti-noise components can be provided on the FPC 88.
Note that in relation to the invention of the present application, Patent document 1 describes that in order to obtain a reactance value in a substrate pattern, as shown in FIG. 6, C-shaped coil patterns 92a to 92d are formed on surfaces of respective layers 91a to 91c of a build-up multi-layer substrate 90, and the coil patterns 92a to 92d are connected by build-up vias 93a to 93c, whereby a helical coil is formed as a whole.